If nothing's plugged in then many devices can indeed be suspended in some way, either by putting them in PCI power state D3hot or by cutting power if the platfo

If nothing's plugged in then many devices can indeed be suspended in some way, either by putting them in PCI power state D3hot or by cutting power if the platform supports it. Plug events are then signaled e.g. by an ACPI GPE (general purpose event, an interrupt sent by the platform to the OS). The case I was referring to was with the Ethernet cable still plugged in. They seem to suspend the Ethernet controller but don't wake it when packets come in, presumably because the controller doesn't support that. The machine appears dead from the outside after a few seconds of inactivity.